Strengthening by gamma/gamma' Interfacial Dislocation Networks in TMS-162--Toward a Fifth-Generation Single-Crystal Superalloy

摘要

Lattice misfit is a common concept in superalloys. A linear relationship between the gamma/gamma' lattice misfit and the strength of Ni-base superalloy exists in the temperature range of 25 deg C to 800 deg C. This low-temperature strengthening effect is believed to be the result of coherency strains in the matrix. Development of single-crystal (SC) superalloys with gamma/gamma' structure increases the temperature capability, because the creep resistance of these gamma/gamma' alloys is much higher than the creep resistance of either the gamma or gamma' materials in bulk form. Especially, at high temperature, the initially cuboidal gamma' particles link up to form platelike precipitates (rafted structure) perpendicular- to the direction of applied stress. Thus, the high-temperature creep mechanism involving dislocation climb around particles will be inhibited by the rafted structure. Shearing of the gamma' phase is also inhibited by gamma/gamma' interfacial dislocation networks. In fact, strengthening a superalloy by the gamma/gamma' interfacial misfit is an important concept in superalloy design. In recent work, we compared several types of superalloys (TMS series) developed in our institute. The study confirmed that the lattice misfit has a close relationship with creep strength for high-temperature low-stress creep deformation. Following such a concept, we have developed a new superalloy TMS-162, which has superior high-temperature creep properties than the fourth-generation SC superalloy TMS-138.